EXPERIMENTAL MEASUREMENT OF FINE THERMOCOUPLE RESPONSE TIME IN AIR RKambiz Farahmand

An experimental apparatus was developed to measure the response time of very fine thermocouples in air. Thermocouple wire size of 0.005 cm in diameter was used. The experiment was performed for air velocities ranging from 0 to 4.11 m/s and small changes in temperature ranging from 24 to 38°C. These experimental conditions were selected to simulate human respiratory conditions. The apparatus produced repeatable square waves and allowed change in direction of temperature gradient without difficulty. The experiment was carried out for both cooling (going from hot to cold) and heating (going from cold to hot) of the thermocouple. Thermocouple response times = 54 ± 3 ms when the thermocouple moved from hot to cold and 56 ± 4 ms when moving from cold to hot. Conduction along thermocouple wire and radiation effects were shown to negligibly affect response times. The effects of the temperature change for small increments and direction of the gradient were also found to be insignificant. There was a positive correlation between air velocity and the time response of a thermocouple. This technique allows investigators a means of assessing data acquisition system response times in a repeatable fashion.